Imaging apparatus and distance information calculation method

ABSTRACT

An imaging apparatus includes a light emitter, a pixel section, and a signal processor which calculates distance information of a subject. The pixel section includes a photoelectric converter, first and second read-out gates, and a plurality of charge accumulators including a first charge accumulator and a second charge accumulator. The first read-out gate is activated in a first period and deactivated in a second period. The second read-out gate is activated in the first period and the second period. The signal processor calculates the distance information based on a total amount of signal charges accumulated in the charge accumulators in the first period and the second period and a difference between an amount of signal charges accumulated in the second charge accumulator in the first period and the second period and an amount of the signal charge accumulated in the first charge accumulator in the first period.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation application of PCT International Application No.PCT/JP2020/005184 filed on Feb. 10, 2020, designating the United Statesof America, which is based on and claims priority of Japanese PatentApplication No. 2019-026055 filed on Feb. 15, 2019. The entiredisclosures of the above-identified applications, including thespecifications, drawings and claims are incorporated herein by referencein their entirety.

FIELD

The present disclosure relates to an imaging apparatus which obtainsdistance information of a subject.

BACKGROUND

Imaging apparatuses which measure distances by a time of flight (TOF)method are known in the related art (see PTL 1, for example).

CITATION LIST Patent Literature

-   PTL 1: Japanese Patent No. 4369574

SUMMARY Technical Problem

In distance measurement by a TOF method, a relatively short distance tothe subject results in a relatively large amount of signal chargesgenerated by photoelectric conversion of reflected light reflected fromthe subject. This may lead to saturation of the charge accumulator whichaccumulates the signal charges in some cases.

Thus, an object of the present disclosure is to provide an imagingapparatus which enables suppression in saturation of the chargeaccumulator.

Solution to Problem

The imaging apparatus according to one aspect of the present disclosureincludes: a light emitter which emits pulsed light to a subject; asolid-state imaging device including a pixel section disposed on asemiconductor substrate; and a signal processor which calculatesdistance information concerning a distance to the subject. The pixelsection includes: a photoelectric converter which converts receivedlight to a signal charge; a first read-out gate and a second read-outgate which read out signal charges from the photoelectric converter; anda plurality of charge accumulators which includes a first chargeaccumulator and a second charge accumulator which are paired with thefirst read-out gate and the second read-out gate, respectively, andaccumulates the signal charges read out by the first read-out gate andthe second read-out gate. The first read-out gate is activated in afirst period which starts before emission of the pulsed light by thelight emitter is stopped, and is deactivated in a second periodsubsequent to the first period, a time interval between the start of thefirst period and an end of the second period is longer than an emissionperiod of the pulsed light, the second read-out gate is activated in thefirst period and the second period, the first charge accumulatoraccumulates the signal charge read out by the first read-out gateactivated in the first period, the second charge accumulator accumulatesthe signal charge read out by the second read-out gate activated in thefirst period and the second period, and when the photoelectric converterreceives light, the signal processor calculates the distance informationbased on: a total amount of the signal charges accumulated in theplurality of charge accumulators in the first period and the secondperiod; and a difference between an amount of the signal chargeaccumulated in the second charge accumulator in the first period and thesecond period and an amount of the signal charge accumulated in thefirst charge accumulator in the first period.

The distance information calculation method according to one aspect ofthe present disclosure is a distance information calculation methodwhich is performed by an imaging apparatus including: a light emitterwhich emits pulsed light to a subject; a solid-state imaging deviceincluding a pixel section disposed on a semiconductor substrate; and asignal processor which calculates distance information concerning adistance to the subject, the pixel section including a photoelectricconverter which converts received light to a signal charge, a firstread-out gate and a second read-out gate which read out signal chargesfrom the photoelectric converter, a plurality of charge accumulatorswhich includes a first charge accumulator and a second chargeaccumulator which are paired with the first read-out gate and the secondread-out gate, respectively, and accumulates the signal charges read outby the first read-out gate and the second read-out gate. The distanceinformation calculation method includes: activating the first read-outgate in a first period which starts before emission of the pulsed lightby the light emitter is stopped, and deactivating the first read-outgate in a second period subsequent to the first period, where a timeinterval between the start of the first period and an end of the secondperiod is longer than an emission period of the pulsed light; activatingthe second read-out gate in the first period and the second period;accumulating the signal charge read out by the first read-out gate whichis activated, in the first charge accumulator in the first period;accumulating the signal charge read out by the second read-out gatewhich is activated, in the second charge accumulator in the first periodand the second period; and calculating the distance information basedon: a total amount of the signal charges accumulated in the plurality ofcharge accumulators in the first period and the second period, and adifference between an amount of the signal charge accumulated in thesecond charge accumulator in the first period and the second period andan amount of the signal charge accumulated in the first chargeaccumulator in the first period when the photoelectric converterreceives light.

Advantageous Effects

An imaging apparatus which enables suppression in saturation of thecharge accumulator is provided.

BRIEF DESCRIPTION OF DRAWINGS

These and other advantages and features will become apparent from thefollowing description thereof taken in conjunction with the accompanyingDrawings, by way of non-limiting examples of embodiments disclosedherein.

FIG. 1 is a block diagram illustrating an example of the configurationof the imaging apparatus according to Embodiment 1.

FIG. 2 is a block diagram illustrating a schematic configuration of thepixel section according to Embodiment 1.

FIG. 3 is a timing chart illustrating an outline (basic principle) ofmeasurement of a distance performed by the imaging apparatus accordingto Embodiment 1.

FIG. 4 is a block diagram illustrating an example of the configurationof the solid-state imaging device according to Embodiment 1.

FIG. 5 is a block diagram illustrating an example of the configurationof the pixel section according to Embodiment 1.

FIG. 6 is an operation sequence diagram of the operation performed bythe imaging apparatus according to Embodiment 1.

FIG. 7 is a timing chart of a first light exposure sequence according toEmbodiment 1.

FIG. 8 is a schematic plan view illustrating how the operation of thesignal charge exchange drive according to Embodiment 1 is performed.

FIG. 9 is a timing chart of drive pulses in the signal charge exchangedrive according to Embodiment 1.

FIG. 10 is a timing chart of a second light exposure sequence accordingto Embodiment 1.

FIG. 11 is a schematic plan view illustrating the signal charge exchangedrive according to Embodiment 1.

FIG. 12 is a timing chart of a third light exposure sequence accordingto Embodiment 1.

FIG. 13 is a timing chart of a fourth light exposure sequence accordingto Embodiment 1.

FIG. 14 is a timing chart of a modified first light exposure sequenceaccording to Embodiment 2.

FIG. 15 is a timing chart of a modified third light exposure sequenceaccording to Embodiment 2.

FIG. 16 is a block diagram illustrating an example of the configurationof the pixel section according to Embodiment 2.

FIG. 17 is an operation sequence diagram of the operation performed bythe imaging apparatus according to Embodiment 3.

FIG. 18 is a schematic plan view illustrating an arrangement relationamong signal charges A0, A1, A2, and A3.

FIG. 19 is a block diagram illustrating an example of the configurationof the pixel section according to Embodiment 4.

FIG. 20 is a timing chart of a first light exposure sequence accordingto Embodiment 4.

FIG. 21 is a timing chart of the first light exposure sequence accordingto Embodiment 4.

FIG. 22 is a timing chart of a third light exposure sequence accordingto Embodiment 4.

DESCRIPTION OF EMBODIMENTS

The imaging apparatus according to one aspect of the present disclosureincludes: a light emitter which emits pulsed light to a subject; asolid-state imaging device including a pixel section disposed on asemiconductor substrate; and a signal processor which calculatesdistance information concerning a distance to the subject. The pixelsection includes: a photoelectric converter which converts receivedlight to a signal charge; a first read-out gate and a second read-outgate which read out signal charges from the photoelectric converter; anda plurality of charge accumulators which includes a first chargeaccumulator and a second charge accumulator which are paired with thefirst read-out gate and the second read-out gate, respectively, andaccumulates the signal charges read out by the first read-out gate andthe second read-out gate. The first read-out gate is activated in afirst period which starts before emission of the pulsed light by thelight emitter is stopped, and is deactivated in a second periodsubsequent to the first period, a time interval between the start of thefirst period and an end of the second period is longer than an emissionperiod of the pulsed light, the second read-out gate is activated in thefirst period and the second period, the first charge accumulatoraccumulates the signal charge read out by the first read-out gateactivated in the first period, the second charge accumulator accumulatesthe signal charge read out by the second read-out gate activated in thefirst period and the second period, and when the photoelectric converterreceives light, the signal processor calculates the distance informationbased on: a total amount of the signal charges accumulated in theplurality of charge accumulators in the first period and the secondperiod; and a difference between an amount of the signal chargeaccumulated in the second charge accumulator in the first period and thesecond period and an amount of the signal charge accumulated in thefirst charge accumulator in the first period.

In the imaging apparatus having such a configuration, the signal chargegenerated through photoelectric conversion of the reflected light of thepulsed light emitted from the light emitter and reflected from thesubject is distributed to and accumulated in the first chargeaccumulator and the second charge accumulator. For this reason, theimaging apparatus having the above configuration can suppress thesaturation of the charge accumulator.

Moreover, a timing for starting activation of the first read-out gatemay be identical to a timing for starting activation of the secondread-out gate.

Moreover, the timing for starting activation of the first read-out gatemay be earlier than the timing for starting activation of the secondread-out gate.

Moreover, the solid-state imaging device may include pixel sectionsarranged in a matrix to constitute a pixel array, each of the pixelsections being the pixel section. In all of the pixel sections, thefirst read-out gates and the second read-out gates may be disposed inidentical relative positions with respect to the photoelectricconverter, and timings of activation and deactivation of the firstread-out gate may be identical, and timings of activation anddeactivation of the second read-out gate may be identical.

Moreover, in a first reflected light non-reception period in which thephotoelectric converter does not receive reflected light of the pulsedlight emitted from the light emitter, the first read-out gate mayfurther be activated in a third period having a time interval identicalto a time interval of the first period, and may further be deactivatedin a fourth period which is subsequent to the third period and has atime interval identical to a time interval of the second period. In thefirst reflected light non-reception period, the second read-out gate mayfurther be activated in the third period and the fourth period, thefirst charge accumulator may further accumulate the signal charge readout by the first read-out gate which is activated, in the third period.The second charge accumulator may further accumulate the signal chargeread out by the second read-out gate which is activated, in the thirdperiod and the fourth period. The signal processor may calculate thedistance information based on an amount of the signal charge accumulatedin the first charge accumulator in the third period and an amount of thesignal charge accumulated in the second charge accumulator in the thirdperiod and the fourth period.

Moreover, the pixel section may further include a signal exchanger foruse in exchanging the signal charge accumulated in the first chargeaccumulator and the signal charge accumulated in the second chargeaccumulator between the first charge accumulator and the second chargeaccumulator. The light emitter may further reemit the pulsed light tothe subject after exchanging the signal charge accumulated in the firstcharge accumulator and the signal charge accumulated in the secondcharge accumulator using the signal exchanger. The second read-out gatemay further be activated in a fifth period where a phase difference inthe fifth period with respect to reemission of the pulsed light by thelight emitter is equal to a phase difference in the first period withrespect to emission of the pulsed light by the light emitter, and mayfurther be deactivated in a sixth period where the phase difference inthe sixth period with respect to reemission of the pulsed light by thelight emitter is equal to a phase difference in the second period withrespect to emission of the pulsed light by the light emitter. The firstread-out gate may further be activated in the fifth period and the sixthperiod. The first charge accumulator may further accumulate the signalcharge read out by the first read-out gate which is activated, in thefifth period and the sixth period. The second charge accumulator mayfurther accumulate the signal charge read out by the second read-outgate which is activated, in the fifth period. When the photoelectricconverter further receives light, the signal processor may calculate thedistance information based on a total amount of the signal chargesaccumulated in the plurality of charge accumulators in the first period,the second period, the fifth period, and the sixth period, and adifference between a total amount of the signal charges accumulated inthe second charge accumulator in the first period and the second periodand the signal charges accumulated in the first charge accumulator inthe fifth period and the sixth period and a total amount of the signalcharge accumulated in the first charge accumulator in the first periodand the signal charge accumulated in the second charge accumulator inthe fifth period.

Moreover, in a second reflected light non-reception period in which thephotoelectric converter does not receive reflected light of the pulsedlight reemitted from the light emitter, the second read-out gate mayfurther be activated in a seventh period having a time intervalidentical to a time interval of the fifth period, and may further bedeactivated in an eighth period which is subsequent to the seventhperiod and has a time interval identical to a time interval of the sixthperiod. In the second reflected light non-reception period, the firstread-out gate may further be activated in the seventh period and theeighth period, the first charge accumulator may further accumulate thesignal charge read out by the first read-out gate which is activated, inthe seventh period and the eighth period. The second charge accumulatormay further accumulate the signal charge read out by the second read-outgate which is activated, in the seventh period. The signal processor maycalculate the distance information based on an amount of the signalcharges accumulated in the first charge accumulator in the seventhperiod and the eighth period and an amount of the signal chargeaccumulated in the second charge accumulator in the seventh period.

Moreover, the plurality of charge accumulators may further include athird charge accumulator and a fourth charge accumulator which arepaired with the first read-out gate and the second read-out gate,respectively.

The distance information calculation method according to one aspect ofthe present disclosure is a distance information calculation methodwhich is performed by an imaging apparatus including: a light emitterwhich emits pulsed light to a subject; a solid-state imaging deviceincluding a pixel section disposed on a semiconductor substrate; and asignal processor which calculates distance information concerning adistance to the subject, the pixel section including a photoelectricconverter which converts received light to a signal charge, a firstread-out gate and a second read-out gate which read out signal chargesfrom the photoelectric converter, a plurality of charge accumulatorswhich includes a first charge accumulator and a second chargeaccumulator which are paired with the first read-out gate and the secondread-out gate, respectively, and accumulates the signal charges read outby the first read-out gate and the second read-out gate. The distanceinformation calculation method includes: activating the first read-outgate in a first period which starts before emission of the pulsed lightby the light emitter is stopped, and deactivating the first read-outgate in a second period subsequent to the first period, where a timeinterval between the start of the first period and an end of the secondperiod is longer than an emission period of the pulsed light; activatingthe second read-out gate in the first period and the second period;accumulating the signal charge read out by the first read-out gate whichis activated, in the first charge accumulator in the first period;accumulating the signal charge read out by the second read-out gatewhich is activated, in the second charge accumulator in the first periodand the second period; and calculating the distance information basedon: a total amount of the signal charges accumulated in the plurality ofcharge accumulators in the first period and the second period, and adifference between an amount of the signal charge accumulated in thesecond charge accumulator in the first period and the second period andan amount of the signal charge accumulated in the first chargeaccumulator in the first period when the photoelectric converterreceives light.

In the distance information calculation method having such aconfiguration, the signal charge generated through photoelectricconversion of the reflected light of the pulsed light emitted from lightemitter and reflected from the subject is distributed to and accumulatedin the first charge accumulator and the second charge accumulator. Forthis reason, the imaging apparatus having the above configuration cansuppress saturation of the charge accumulator.

Specific examples of the imaging apparatus according to one aspect ofthe present disclosure will now be described with reference to thedrawings. The embodiments shown here are all illustrations of specificexamples of the present disclosure. Accordingly, numeric values, shapes,components, arrangements of the components, connections forms thereof,and the like shown in the embodiments below are exemplary and should notbe construed as limitations to the present disclosure. The drawings areschematic views, and are not always strictly illustrated.

Embodiment 1

The imaging apparatus according to Embodiment 1 will now be described.The imaging apparatus measures a distance by a TOF method using theround trip time of flight of light to a subject. Here, first, the basicprinciple of the distance measurement performed by the imaging apparatusaccording to Embodiment 1 will be described, and then a specificconfiguration of the imaging apparatus according to Embodiment 1 will bedescribed. The imaging apparatus according to Embodiment 1 is alsoreferred to as distance measurement imaging apparatus in some casesbecause it measures the distance to a subject. 1. Basic Principle

FIG. 1 is a block diagram illustrating an example of the configurationof imaging apparatus 1 according to Embodiment 1. FIG. 2 is a blockdiagram illustrating a schematic configuration of pixel section 100included in imaging apparatus 1.

As illustrated in FIG. 1 , imaging apparatus 1 includes light emitter 4,solid-state imaging device 10, signal processor 2, and controller 3.

Controller 3 outputs a light emission signal to instruct irradiation ofa subject with light, and a light exposure signal to instruct exposureto background light attributed to reflected light from the subject andsunlight. For example, controller 3 is implemented by a memory and aprocessor which executes programs stored in the memory.

Light emitter 4 includes a light emitting element, and emits pulsedlight to the subject according to the light emission signal output fromcontroller 3. The light emitting element is implemented by a laserdiode, a vertical cavity surface emitting laser (VCSEL), or a lightemitting diode (LED), for example. The irradiation light is infraredlight, for example.

Solid-state imaging apparatus 10 includes pixel array 20 including pixelsections 100 arranged in a matrix (see FIG. 2 ). For example,solid-state imaging device 10 is implemented by a CMOS image sensor.

Pixel array 20 receives reflected light of the pulsed light emitted fromlight emitter 4 and reflected from the subject. Pixel array 20 alsoreceives background light attributed to sunlight or the like. Pixelarray 20 is exposed to light according to the light exposure signaloutput from controller 3. Although pixel array 20 including pixelsections 100 arranged in a matrix will be described below, pixel array20 can have any other configuration than the configuration where pixelsections 100 arranged in a matrix is included, as long as at least onepixel section 100 is included. For example, pixel array 20 may includeone pixel section 100.

Pixel section 100 is disposed above a semiconductor substrate. Asillustrated in FIG. 2 , pixel section 100 includes photoelectricconverter 101, first read-out gate 106 a, second read-out gate 106 b,first charge accumulator 102 a, and second charge accumulator 102 b.

Photoelectric converter 101 converts the received light to a signalcharge. For example, photoelectric converter 101 is implemented by aphotodiode.

First read-out gate 106 a and second read-out gate 106 b read out signalcharges from photoelectric converter 101. First read-out gate 106 a andsecond read-out gate 106 b are in one of the activated state, i.e., anelectrically conducted state and a deactivated state, i.e., anelectrically unconducted state. First read-out gate 106 a and secondread-out gate 106 b perform the signal charge reading-out in theactivated state, and do not perform the signal charge reading-out in thedeactivated state. First read-out gate 106 a and second read-out gate106 b are individually controlled between the electrically conductedstate and the electrically unconducted state according to the lightexposure signal output from controller 3.

First charge accumulator 102 a and second charge accumulator 102 b arecharge accumulators which are paired with first read-out gate 106 a andsecond read-out gate 106 b to accumulate signal charges read out byfirst read-out gate 106 a and second read-out gate 106 b, respectively.The description will be performed here, for convenience, where firstcharge accumulator 102 a accumulates a signal charge read out by firstread-out gate 106 a and second charge accumulator 102 b accumulates asignal charge read out by second read-out gate 106 b.

Returning to FIG. 1 , the description of the configuration of imagingapparatus 1 will be continued.

Signal processor 2 calculates distance information concerning thedistance to the subject based on the signal charge accumulated in firstcharge accumulator 102 a and signal charge accumulated in second chargeaccumulator 102 b. For example, signal processor 2 is implemented by amemory and a processor which executes programs stored in the memory.

Although signal processor 2 and controller 3 have been described here asexternal components of solid-state imaging device 10, part or all of thefunctions implemented by signal processor 2 may be implemented bysolid-state imaging device 10, or part or all of the functionsimplemented by controller 3 may be implemented by solid-state imagingdevice 10.

FIG. 3 is a timing chart illustrating the outline (basic principle) ofthe distance measurement performed by imaging apparatus 1 having theabove configuration.

The pulsed irradiation light having time width Tp, which is emitted fromlight emitter 4 in response to an instruction by controller 3, reachespixel section 100 as reflected light reflected from the subject with adelay of time Td from the light emission timing of the irradiationlight.

The relation between time Td and distance D is represented by thefollowing expression:D=c×Td/2  (Expression 0)

where the distance to the subject is defined as D and the speed of light(299,792,458 m/s) is defined as c.

Controller 3 controls a first light exposure period (also referred to as“first period”) in which first read-out gate 106 a and second read-outgate 106 b are activated and a second light exposure period (alsoreferred to as “second period”) in which only second read-out gate 106 bis activated, the second period being subsequent to the first lightexposure period. Here, the first light exposure period is defined as aperiod from the start of light emission by light emitter 4 to the endthereof. The second light exposure period is defined as a period fromthe end of the light emission by light emitter to passing of anothertime Tp. Here, assume that the signal charge reading-out ability offirst read-out gate 106 a is equal to that of second read-out gate 106b.

As shown by “Signal charge in first charge accumulator” and “Signalcharge in second charge accumulator” in FIG. 3 , halves of the chargeamount of the charge generated in photoelectric converter 101 in thefirst light exposure period in which first read-out gate 106 a andsecond read-out gate 106 b are both in the activated state aredistributed and transferred to first charge accumulator 102 a and secondcharge accumulator 102 b, respectively. The charge generated inphotoelectric converter 101 in the second light exposure period in whichonly second read-out gate 106 b is in the activated state is totallytransferred to second charge accumulator 102 b.

In such an operation for the pulsed irradiation light at one time, wherethe signal charge generated from the total pulsed reflected light inphotoelectric converter 101 is defined as Sr, the signal chargeaccumulated in first charge accumulator 102 a is defined as Sa, and thesignal charge accumulated in second charge accumulator 102 b is definedas Sb, the sum of signal charge Sa and signal charge Sb corresponds tosignal charge Sr, and the difference between signal charge Sa and signalcharge Sb corresponds to the signal charge (hereinafter, referred to asSd) corresponding to the reflected light which reaches pixel section 100in the second light exposure period.

Because the ratio of time Td to time Tp is equal to the ratio of signalcharge Sd to signal charge Sr, signal processor 2 can calculate thedistance D to the subject from the following expression:D=c×Tp/2×(Sd/Sr)  (Expression 1)D=c×Tp/2×(Sb−Sa)/(Sb+Sa)  (Expression 2)

A specific configuration of imaging apparatus 1 which performs thedistance measurement according to the outline (basic principle) will nowbe described.

2. Specific Configuration

FIG. 4 is a block diagram illustrating an example of the configurationof solid-state imaging device 10 according to Embodiment 1.

As illustrated in FIG. 4 , solid-state imaging device 10 includes pixelarray 20, pixel array controller 11, vertical scanner 12, columnprocessor 13, horizontal scanner 14, and output buffer 15.

Pixel array 20 includes pixel sections 100 arranged in a matrix, and aplurality of vertical signal lines 16 disposed in corresponding columns.Here, pixel sections 100 included in pixel array 20 are arranged in amatrix such that first read-out gates 106 a and second read-out gates106 b are disposed in identical relative positions with respect tophotoelectric converter 101 in all of pixel sections 100.

Pixel array 20 includes transfer channel 17 formed for each column bylinearly connecting transfer channels 104 (described later) in thecolumn direction, transfer channels 104 being included in each of pixelsections 100 aligned in the column direction. Pixel array controller 11controls pixel sections 100 included in pixel array 20, based on thelight exposure signal output from controller 3. Here, pixel arraycontroller 11 controls pixel sections 100 such that the timings ofactivation and deactivation of first read-out gates 106 a are identicaland the timings of activation and deactivation of second read-out gates106 b are identical in all of pixel sections 100 included in pixel array20.

Vertical scanner 12 scans the signal charges read out by pixel sections100 included in pixel array 20 in row unit. In other words, verticalscanner 12 sequentially selects the rows one by one, and outputs thesignal charges to the corresponding one of vertical signal lines 16disposed for the respective columns.

Column processor 13 receives the signal charges output to verticalsignal lines 16, and performs correlated double sampling (CDS) to outputtheir corresponding pixel signals.

Horizontal scanner 14 scans the pixel signals output from columnprocessor 13, namely, sequentially selects and outputs the pixel signalsone by one. In some cases, column processor 13 may include an A/Dconversion circuit which converts the pixel signal to digital signal foreach column of vertical signal line 16.

Output buffer 15 outputs the pixel signals received from horizontalscanner 14.

FIG. 5 is a schematic view illustrating an example of the configurationof pixel section 100.

As illustrated in FIG. 5 , pixel section 100 includes photoelectricconverter 101, a plurality of charge accumulators 102 (as one example,first charge accumulator 102 a and second charge accumulator 102 b), aplurality of read-out gates 106 (as one example, first read-out gate 106a and second read-out gate 106 b), output control gate 113, floatingdiffusion layer 114, reset gate 115, reset drain 116, read-out circuit117, a plurality of light exposure control gates 108 (as one example,light exposure control gate 108 a and light exposure control gate 108b), a plurality of overflow drains 109 (as one example, overflow drain109 a and overflow drain 109 b), and signal exchanger 110.

Photoelectric converter 101 converts the received light to a signalcharge.

Read-out gate 106 reads out the signal charge from photoelectricconverter 101.

Charge accumulator 102 accumulates the signal charge read out byread-out gate 106. Charge accumulator 102 includes transfer channel 104(CCD channel 104) for transferring the signal charge disposed under agate insulating film and transfer electrode 105 (as one example, any oneof transfer electrodes 105 a, 105 b, 105 c, 105 d, and 105 e) disposedabove the gate insulating film. In other words, as illustrated in FIG. 5, charge accumulator 102 includes part of transfer channel 104 and partof transfer electrode 105 which overlaps part of transfer channel 104 ina planar view of the semiconductor substrate. As illustrated in FIG. 5 ,one transfer channel 104 is disposed per pixel section 100. As describedabove, in pixel array 20, transfer channels 104 for pixel sections 100aligned in the column direction are linearly connected one another inthe column direction. Thereby, transfer channel 17 is formed for eachcolumn of pixel array 20.

In the present embodiment, the voltages applied to transfer electrodes105 a, 105 b, 105 c, 105 d, and 105 e are defined as VG1, VG2, VG3, VG4,and VG5, respectively.

First charge accumulator 102 a and second charge accumulator 102 bperform 5-phase drive. When high voltages VG1 and VG3 are applied bypixel array controller 11, first charge accumulator 102 a and secondcharge accumulator 102 b are formed adjacent to first read-out gate 106a and second read-out gate 106 b, respectively, below transfer electrode105 in the depth direction thereof (here, below transfer electrode 105 aand transfer electrode 105 c in the depth directions thereof).

Overflow drain 109 discharges the signal charge from photoelectricconverter 101.

Light exposure control gate 108 controls the discharge of the signalcharge to overflow drain 109.

Signal exchanger 110 receives a transfer of the signal charge to beaccumulated in charge accumulator 102 from one of the plurality ofcharge accumulators 102 (here, first charge accumulator 102 a and secondcharge accumulator 102 b), retains the signal charge, and transfers asignal charge already retained to one of the plurality of chargeaccumulators 102 (here, first charge accumulator 102 a and second chargeaccumulator 102 b). Signal exchanger 110 includes charge retention gate111, and transfer control gate 112 which controls transfer by signalexchanger 110. As described later, signal exchanger 110 is used toexchange the signal charge accumulated in one charge accumulator (here,first charge accumulator 102 a or second charge accumulator 102 b) ofthe plurality of charge accumulators 102 and the signal chargeaccumulated in the other charge accumulator (here, second chargeaccumulator 102 b or first charge accumulator 102 a) of the plurality ofcharge accumulators 102 between the one charge accumulator (here, firstcharge accumulator 102 a or second charge accumulator 102 b) and theother charge accumulator (here, second charge accumulator 102 b or firstcharge accumulator 102 a).

Floating diffusion layer 114 receives the transfer of the signal chargeto be accumulated in charge accumulator 102 from one of the plurality ofcharge accumulators 102 (here, first charge accumulator 102 a and secondcharge accumulator 102 b).

Output control gate 113 controls the transfer to floating diffusionlayer 114.

Read-out circuit 117 converts the signal charge retained in floatingdiffusion layer 114 to a voltage, and reads out the voltage from pixelsection 100 to vertical signal line 16. For example, read-out circuit117 includes a source follower transistor including a gate connected tofloating diffusion layer 114, and a selection transistor connected tothe source follower transistor in series. For example, after theselection transistor selects read-out circuit 117, the signal chargeretained in floating diffusion layer 114 is converted to a voltagesignal by read-out circuit 117, and is read out to vertical signal line16.

Pixel array controller 11 applies drive pulse ODG to light exposurecontrol gate 108 a and light exposure control gate 108 b, drive pulsesTG1 and TG2 to first read-out gate 106 a and second read-out gate 106 b,and drive pulses VG1 to VG5 to transfer electrodes 105 a to 105 e.During light exposure, a high voltage is applied to electrodescorresponding to VG1 and VG3, and a low voltage is applied to otherelectrodes. Thereby, the charge can be accumulated under transferelectrode 105 to which a high voltage is applied. In other words, chargeaccumulators 102 (here, first charge accumulator 102 a and second chargeaccumulator 102 b) are formed by transfer electrodes 105 to which a highvoltage is applied (here, transfer electrode 105 a and transferelectrode 105 c) and transfer channel 104 underlying and overlapping theelectrodes.

In the initial state, ODG is in a high state, and photoelectricconverter 101 is reset. First read-out gate 106 a and second read-outgate 106 b are in a low state. First charge accumulator 102 a and secondcharge accumulator 102 b including transfer electrode 105 a and transferelectrode 105 c retained in the high state are electrically shieldedfrom photoelectric converter 101. In this state, the signal chargegenerated in photoelectric converter 101 is discharged to overflow drain109 through light exposure control gate 108.

The operation performed by imaging apparatus 1 will now be describedwith reference to the drawings.

FIG. 6 is an operation sequence diagram illustrating the operationperformed by imaging apparatus 1.

As illustrated in FIG. 6 , imaging apparatus 1 performs the stepsincluded in a first light exposure sequence, signal charge exchangedrive, a second light exposure sequence, reading-out of an irradiationlight exposure signal, a third light exposure sequence, signal chargeexchange drive, a fourth light exposure sequence, reading-out of anon-irradiation light exposure signal, and calculation of the distancein this order.

First, the first light exposure sequence will be described.

FIG. 7 is a timing chart of the first light exposure sequenceillustrating the light emission timing of light emitter 4, the lightemission and signal accumulation timing in pixel section 100, and thelight exposure states of the signal charges accumulated in chargeaccumulators 102 through first read-out gate 106 a and second read-outgate 106 b.

The first light exposure sequence includes a first light exposure period(also referred to as “first period”) synchronizing with time Tp from thestart of irradiation to the end of irradiation with pulsed light emittedfrom light emitter 4 having a timing controlled by controller 3, and asecond light exposure period (also referred to as “second period”) untiltime Tp passes from the end of irradiation with the pulsed light. Asillustrated in FIG. 7 , the first period starts before the irradiationwith the pulsed light by light emitter 4 stops. The second period is aperiod subsequent to the first light exposure period. In this period,the time interval between the start of the first light exposure periodand the end of the second period is longer than emission period Tp ofthe pulsed light.

After the first light exposure sequence starts, the pulsed light havingan interval of time Tp is emitted from light emitter 4 according to aninstruction by controller 3. The reflected light of the emitted pulsedlight reflected from the subject reaches pixel section 100 after a delayof time Td according to the distance from imaging apparatus 1, and isconverted to a signal charge in photoelectric converter 101.

According to an instruction by controller 3, pixel array controller 11transits ODG from the high state (activated state) to the low state(deactivated state) synchronizing with time t11 at which the first lightexposure period starts, and concurrently transits first read-out gate106 a and second read-out gate 106 b from the low state (deactivatedstate) to the high state (activated state).

By the operation of pixel array controller 11, discharge of the signalcharge from photoelectric converter 101 to overflow drain 109 isstopped, and the signal charge generated in photoelectric converter 101by receiving an early arriving component of the reflected light of thepulsed light emitted from light emitter 4 which reaches photoelectricconverter 101 in the first light exposure period and by receiving thebackground light other than the reflected light reaching there in thefirst light exposure period is accumulated in first charge accumulator102 a through first read-out gate 106 a and in second charge accumulator102 b through second read-out gate 106 b.

Next, in the second light exposure period, according to an instructionby controller 3, pixel array controller 11 transits first read-out gate106 a from the high state (activated state) to the low state(deactivated state) at time t12 (timing of the start). Thereby, theaccumulation of the signal charge in first charge accumulator 102 a isstopped.

By the control operation described above, the signal charge generated inphotoelectric converter 101 by receiving a lately arriving component ofthe reflected light which reaches photoelectric converter 101 after timet12 in the second light exposure period and by receiving the backgroundlight which reaches photoelectric converter 101 in the second lightexposure period is totally accumulated in second charge accumulator 102b through second read-out gate 106 b.

At time t13, which is the end of the second light exposure period,according to an instruction by controller 3, pixel array controller 11stops the accumulation of the signal charge in second charge accumulator102 b by transiting second read-out gate 106 b from the high state(activated state) to the low state (deactivated state), and convertslight exposure control gate 108 to an electrically conducted state bytransiting ODG from the low state (deactivated state) to the high state(activated state). Thereby, photoelectric converter 101 is reset.

At the end of the first light exposure sequence, the relationsrepresented by the following expressions are established:A0=S1A  (Expression 3)A1=S1B  (Expression 4)where the signal charge accumulated in charge accumulator 102 throughfirst read-out gate 106 a is defined as S1A, the signal chargeaccumulated in charge accumulator 102 through second read-out gate 106 bis defined as S1B, the signal charge accumulated in first chargeaccumulator 102 a is defined as A0, and the signal charge accumulated insecond charge accumulator 102 b is defined as A1.

Furthermore, signal charge S1A is made of signal charge S1Ar generatedin photoelectric converter 101 by receiving the pulsed reflected lightand signal charge S1Ab generated in photoelectric converter 101 byreceiving the background light other than the pulsed reflected light,and signal charge S1B is made of signal charge S1Br generated inphotoelectric converter 101 by receiving the pulsed reflected light andsignal charge S1Bb generated in photoelectric converter 101 by receivingthe background light other than the pulsed reflected light. Thus, therelations represented by the following expressions are established:A0=S1Ar+S1Ab  (Expression 5)A1=S1Br+S1Bb  (Expression 6)

As described above, in the first light exposure sequence, the charge isconcurrently transferred to two charge accumulators 102, i.e., firstcharge accumulator 102 a and second charge accumulator 102 b in thefirst light exposure period, and about a half of the charge amount ofthe signal charge generated in photoelectric converter 101 in the firstlight exposure period is accumulated in their corresponding chargeaccumulators 102. Thus, signal saturation in charge accumulator 102 issuppressed.

Furthermore, there is a fundamental phenomenon as follows: The intensityof the reflected light is proportional to distance D to the subject by1/D². Thus, a subject located in a short distance has smaller delay timeTd of the reflected light, resulting in a larger proportion of the earlyarriving component of the reflected light included in the first lightexposure period. In the present disclosure, about a half of the signalcharge generated in photoelectric converter 101 from the early arrivingcomponent of the reflected light, which is included in the first lightexposure period and has an intensity increased by the subject located ina shorter distance, is distributed to and accumulated in chargeaccumulators 102. For this reason, it is shown that the control of lightemission and light exposure in the first light exposure sequenceprovides a high effect of suppressing the signal saturation in chargeaccumulator 102 for the subject located in a short distance.

To be noted, a difference in charge transfer properties between firstread-out gate 106 a and second read-out gate 106 b caused by a variationin properties in the semiconductor production process may lead to apossibility that the amount of the signal charge accumulated in firstcharge accumulator 102 a in the first light exposure period and that ofthe signal charge accumulated in second charge accumulator 102 b in thefirst light exposure period are not exactly 50% of the charge amount ofthe signal charge generated in photoelectric converter 101 in the firstlight exposure period.

Next, the signal charge exchange drive will be described.

FIG. 8 is a schematic plan view illustrating how the operation of thesignal charge exchange drive is performed.

FIG. 9 is a timing chart of the drive pulses in the signal chargeexchange drive.

In FIG. 8 , drive pulses VG1 to VG5 are applied to transfer electrodes105 a to 105 e by pixel array controller 11. Thereby, the signal chargescan be transferred to desired positions. Drive pulses VS and VB areapplied to charge retention gate 111 and transfer control gate 112,respectively, by pixel array controller 11.

In FIG. 8 , for easy understanding of a change in position of thetransferred signal charge, signal charge A0 and signal charge A1generated in a specific pixel section 100 are represented by hatchedoval shapes which indicate the positions of the signal charges.

Initially, VG1 and VG3 are controlled to a high voltage at time tt1(namely, time t13 in FIG. 7 ) at which the first light exposure sequenceis completed. Thereby, signal charge A0 and signal charge A1 areaccumulated under transfer electrodes 105 (here, transfer electrodes 105a and 105 c) to which VG1 and VG3 are applied, respectively.

Next, VG5 and VG2 are controlled to a high voltage at time tt2. Thereby,signal charge A0 and signal charge A1 are accumulated under transferelectrodes 105 (here, transfer electrodes 105 e and 105 b) to which VG5and VG2 are applied. In other words, signal charge A0 accumulated underthe transfer electrode (here, transfer electrode 105 a) to which VG1 isapplied at time tt1 is transferred to under transfer electrode 105(here, transfer electrode 105 e) to which VG5 is applied, and signalcharge A1 accumulated under the transfer electrode (here, transferelectrode 105 c) to which VG3 is applied at time tt1 is transferred tounder transfer electrode 105 (here, transfer electrode 105 b) to whichVG2 is applied. Next, as illustrated in FIG. 9 , VS is controlled to ahigh voltage, and then VB is controlled to a high voltage. Thereby, acharge transfer path is formed between signal exchanger 110 and chargeaccumulator 102 of transfer electrode 105 (here, transfer electrode 105e) to which VG5 is applied. Subsequently, a low voltage is sequentiallyapplied to VG5 and VB to transfer signal charge A0 to under chargeretention gate 111 (tt3). As described above, pixel array controller 11outputs a first signal for transferring the signal charge accumulated inone of charge accumulators 102 from the one of charge accumulators 102to signal exchanger 110.

Next, at time tt3, signal charge A1 located in a lower position in FIG.8 is transferred to an upper position with respect to signal charge A0accumulated under charge retention gate 111 by 5-phase drive. Signalcharge A1 is moved across charge retention gate 111 to under transferelectrode 105 to which VG3 is applied (tt4).

Subsequently, VG5 and VB are controlled to a high voltage again.Thereby, a charge transfer path is formed between signal exchanger 110and charge accumulator 102 in transfer electrode 105 (here, transferelectrode 105 e) to which VG5 is applied. Subsequently, a low voltage issequentially applied to VS and VB, and then signal charge A0 istransferred to under transfer electrode 105 (here, transfer electrode105 e) to which VG5 is applied (tt5). Thus, pixel array controller 11outputs a second signal for transferring the signal charge accumulatedin signal exchanger 110 from signal exchanger 110 to one of chargeaccumulators 102.

Next, signal charge A0 and signal charge A1 are transferred by 5-phasedrive downwardly in FIG. 8 , so that signal charge A0 and signal chargeA1 are moved to exchange the positions at time tt1. Hereinafter, thisseries of operations is called a signal charge exchange operation. Asdescribed above, by outputting a drive signal including the first signaland the second signal, pixel array controller 11 can move signal chargeA0 accumulated in charge accumulator 102 through first read-out gate 106a in the first light exposure sequence to second charge accumulator 102b and can move signal charge A1 accumulated in charge accumulator 102through second read-out gate 106 b in the first light exposure sequenceto first charge accumulator 102 a.

Next, the second light exposure sequence will be described.

FIG. 10 is a timing chart of the second light exposure sequence showingthe light emission timing of light emitter 4, the light exposure andsignal accumulation timing in pixel section 100, and the light exposurestates of the respective signal charges accumulated in chargeaccumulators 102 through first read-out gate 106 a and second read-outgate 106 b.

Immediately before the second light exposure sequence starts, firstcharge accumulator 102 a retains signal charge A1 generated in the firstlight exposure sequence and second charge accumulator 102 b retainssignal charge A0 generated in the first light exposure sequence.

As in the first light exposure sequence, the second light exposuresequence also includes a first light exposure period (also referred toas “fifth period”) synchronizing with time Tp from the start ofirradiation to the end of irradiation with the pulsed light emitted fromlight emitter 4 having a timing controlled by controller 3, and a secondlight exposure period (also referred to as “sixth period”) until time Tppasses from the end of irradiation with the pulsed light. As illustratedin FIGS. 7 and 10 , the phase difference in the fifth period withrespect to emission of the pulsed light by light emitter 4 is equal tothat in the first period with respect to emission of the pulsed light bylight emitter 4. The phase difference in the sixth period with respectto emission of the pulsed light by light emitter 4 is equal to that inthe second period with respect to emission of the pulsed light by lightemitter 4.

After the first light exposure period starts, pulsed light having aninterval of time Tp is emitted from light emitter 4 according to aninstruction by controller 3. The reflected light of the emitted pulsedlight reflected from the subject reaches pixel section 100 after a delayof time Td according to the distance from imaging apparatus 1, and isconverted to a signal charge in photoelectric converter 101.

According to an instruction by controller 3, pixel array controller 11transits ODG from a high state (activated state) to a low state(deactivated state) synchronizing with time t11 at which the first lightexposure period starts, and concurrently transits first read-out gate106 a and second read-out gate 106 b from the low state (deactivatedstate) to the high state (activated state).

By the operation of pixel array controller 11, discharge of the signalcharge from photoelectric converter 101 to overflow drain 109 isstopped, and the signal charge generated in photoelectric converter 101by receiving an early arriving component of the reflected light of thepulsed light emitted from light emitter 4 which reaches photoelectricconverter 101 in the first light exposure period and by receiving thebackground light other than the reflected light reaching there in thefirst light exposure period is accumulated in first charge accumulator102 a through first read-out gate 106 a and in second charge accumulator102 b through second read-out gate 106 b.

Next, in the second light exposure period, according to an instructionby controller 3, pixel array controller 11 transits second read-out gate106 b from the high state (activated state) to the low state(deactivated state) at time t22 (timing of the start). Thereby, theaccumulation of the signal charge in second charge accumulator 102 b isstopped.

By the control operation described above, the signal charge generated inphotoelectric converter 101 by receiving a lately arriving component ofthe reflected light which reaches photoelectric converter 101 after timet22 in the second light exposure period and by receiving the backgroundlight which reaches photoelectric converter 101 in the second lightexposure period is totally accumulated in first charge accumulator 102 athrough first read-out gate 106 a.

At time t23, which is the end of the second light exposure period,according to an instruction by controller 3, pixel array controller 11stops the accumulation of the signal charge in first charge accumulator102 a by transiting first read-out gate 106 a from the high state(activated state) to the low state (deactivated state), and convertslight exposure control gate 108 to an electrically conducted state bytransiting ODG from the low state (deactivated state) to the high state(activated state). Thereby, photoelectric converter 101 is reset.

At the end of the second light exposure sequence, signal charge A1accumulated in the first light exposure sequence before the start of thesecond light exposure sequence is accumulated in first chargeaccumulator 102 a and signal charge A0 accumulated in the first lightexposure sequence before the start of the second light exposure sequenceis accumulated in second charge accumulator 102 b. Thus, the relationsrepresented by the following expressions are established for signalcharge A0 and signal charge A1 after second light exposure sequence iscompleted:A0=S1A+S2BA1=S1B+S2Awhere the signal charge accumulated in charge accumulator 102 throughfirst read-out gate 106 a is defined as S2A and the signal chargeaccumulated in charge accumulator 102 through second read-out gate 106 bis defined as S2B.

Furthermore, signal charge S2A is made of signal charge S2Ar generatedin photoelectric converter 101 by receiving the pulsed reflected lightand signal charge S2Ab generated in photoelectric converter 101 byreceiving the background light other than the pulsed reflected light,and signal charge S2B is made of signal charge S2Br generated inphotoelectric converter 101 by receiving the pulsed reflected light andsignal charge S2Bb generated in photoelectric converter 101 by receivingthe background light other than the pulsed reflected light. Thus, therelations represented by the following expressions are established:A0=(S1Ar+S2Br)+(S1Ab+S2Bb)  (Expression 7)A1=(S1Br+S2Ar)+(S1Bb+S2Ab)  (Expression 8)

Signal charge A0 obtained as a result of the first light exposuresequence and the second light exposure sequence is made of a componentobtained through addition average of signal charge S1Ar accumulatedthrough first read-out gate 106 a and signal charge S2Br accumulatedthrough second read-out gate 106 b out of the signal charges generatedin photoelectric converter 101 by receiving the pulsed reflected lightin the first light exposure periods of the first and second lightexposure sequences, and a component obtained through addition average ofsignal charge S1Ab accumulated through first read-out gate 106 a andsignal charge S2Bb accumulated through second read-out gate 106 b out ofthe signal charges generated in photoelectric converter 101 by receivingthe background light other than the pulsed reflected light in the firstlight exposure periods of the first and second light exposure sequences.Such a configuration provides signal charge A0 obtained as a result ofthe first light exposure sequence and the second light exposure sequenceas a signal charge such that the difference in transfer propertiescaused by a variation in properties in the semiconductor productionprocess between first read-out gate 106 a and second read-out gate 106 bare smoothed and cancelled.

As in signal charge A0, this configuration also provides signal chargeA1 obtained as a result of the first light exposure sequence and thesecond light exposure sequence as a signal charge such that thedifference in transfer properties caused by a variation in properties inthe semiconductor production process between first read-out gate 106 aand second read-out gate 106 b are smoothed and cancelled.

From above, component (S1Ar+S2Br) of signal charge A0 corresponding tothe early arriving component of the reflected light and a component ofreflected light component (S1Br+S2Ar) of signal charge A1 accumulated inthe first light exposure period have the same charge amount because thedifferences in transfer properties between first read-out gate 106 a andsecond read-out gate 106 b are cancelled.

FIG. 11 is a schematic plan view illustrating how the operation of thesignal charge exchange drive is performed in the case where signalcharge A1 is accumulated under transfer electrode 105 (here, transferelectrode 105 a) to which VG1 is applied and signal charge A0 isaccumulated under transfer electrode 105 (here, transfer electrode 105c) to which VG3 is applied.

By performing the operation to exchange the signal charges illustratedin FIG. 11 after the end of the second light exposure sequence, signalcharge A0 and signal charge A1 can be returned to the originalaccumulation positions in the first light exposure sequence. Thisoperation to exchange the signal charges is also referred to as exchangedrive for returning the signal charge.

The operation of exposure to reflected light can be performed severaltimes by repeating the “first light exposure sequence”, the “signalcharge exchange drive”, the “second light exposure sequence”, and the“exchange drive for returning the signal charge” several times. This canreduce unevenness in amount of the signal charge of the background lightcomponent in the case where the light quantity of the background lightvaries according to the time, for example.

Next, reading-out of the irradiation light exposure signal will bedescribed.

In the reading-out of the irradiation light exposure signal, signalcharges A0 and signal charges A1 obtained in respective pixel sections100 by performing the first light exposure sequence and the second lightexposure sequence are output from solid-state imaging device 10 tosignal processor 2. This step is started after the second light exposuresequence is completed. According to an instruction by controller 3, forall of the pixel sections 100, pixel array controller 11 moves signalcharges A0 retained in second charge accumulators 102 b to undertransfer electrodes 105 d, to which VG4 is applied, by charge transferaccompanied by application of the 5-phase drive pulses VG1 to VG5applied to transfer electrodes 105 a to 105 e.

According to an instruction by pixel array controller 11, inpredetermined one column of pixel sections 100, vertical scanner 12discharges unnecessary residual charges in floating diffusion layers 114to reset drains 116 by activating reset gates 115 while output controlgates 113 are in the deactivated state, and then outputs non-signalvoltage outputs to vertical signal line 16 by activating read-outcircuits 117.

According to an instruction by vertical scanner 12, column processor 13retains the non-signal voltages output to the corresponding verticalsignal lines 16 of the respective columns.

Next, in the same one column of pixel sections 100, vertical scanner 12discharges unnecessary residual charges in floating diffusion layers 114to reset drains 116 by activating reset gates 115 while output controlgates 113 are in the deactivated state, transfers signal charges A0retained under transfer electrodes 105 d to floating diffusion layers114 by activating output control gates 113, and then outputs the signalvoltage outputs of signal charges A0 to vertical signal line 16 byactivating read-out circuits 117.

According to an instruction by vertical scanner 12, column processor 13performs correlated double sampling from the non-signal voltages of thecolumns previously retained and the signal voltages of signal chargesA0, and outputs and retains pixel signals A0 of the respective columnsto and in horizontal scanner 14.

According to an instruction by vertical scanner 12, horizontal scanner14 sequentially selects pixel signals A0 corresponding to pixel sections100 in a predetermined column in the horizontal direction bysequentially scanning groups of pixel signals A0 for one column outputfrom column processor 13 and retained in horizontal scanner 14, andoutputs pixel signals A0 to signal processor 2 through output buffer 15.

Vertical scanner 12 successively, column by column, performs a series ofoperations from control of the output of the non-signal voltage tocontrol of the output of pixel signals A0 for one column by horizontalscanner 14, and outputs all the pixel signals A0 of corresponding pixelsections 100 from solid-state imaging device 10 through output buffer 15by raster scanning.

According to an instruction by controller 3, signal processor 2temporarily retains pixel signals A0 of all of the pixel sections 100output from solid-state imaging device 10 by raster scanning.

Next, for all of the pixel sections 100, pixel array controller movessignal charges A1 retained in second charge accumulators 102 b totransfer electrodes 105 d, to which VG4 is applied, by charge transferaccompanied by application of the 5-phase drive pulses VG1 to VG5applied to transfer electrodes 105 a to 105 e. Subsequently, the sameoperation as that in the control of the output of pixel signal A0 isperformed, and all the pixel signals A1 of corresponding pixel sections100 are output from solid-state imaging device 10 through output buffer15 by raster scanning.

According to an instruction by controller 3, signal processor 2temporarily retains pixel signals A1 of all the pixel sections 100output from solid-state imaging device 10 by raster scanning.

Next, a third light exposure sequence will be described.

FIG. 12 is a timing chart of the third light exposure sequence showingthe light emission timing of light emitter 4, the light exposure andsignal accumulation timing in pixel section 100, and the light exposurestates of the respective signal charges accumulated in chargeaccumulators 102 through first read-out gate 106 a and second read-outgate 106 b.

The third light exposure sequence includes a first light exposure period(also referred to as “third period”) having the same length as that oftime Tp from the start of irradiation to the end of irradiation withpulsed light from light emitter 4 in the first light exposure sequenceand a second light exposure period (also referred to as “fourth period”)until time Tp passes from the end of the first light exposure period. Asillustrated in FIGS. 7 and 11 , the third period has the same timeinterval as that of the first period, and the fourth period has the sametime interval as that of the second period.

In the third light exposure sequence, the pulsed light is not emittedfrom light emitter 4.

After the third light exposure sequence starts, according to aninstruction by controller 3, pixel array controller 11 transits ODG fromthe high state (activated state) to the low state (deactivated state)synchronizing with time t31 at which the first light exposure periodstarts, and concurrently transits first read-out gate 106 a and secondread-out gate 106 b from the low state (deactivated state) to the highstate (activated state).

By the operation performed by pixel array controller 11, the dischargeof the signal charge from photoelectric converter 101 to overflow drain109 is stopped, and the signal charge generated in photoelectricconverter 101 by receiving the background light which reachesphotoelectric converter 101 in the first light exposure period isaccumulated in first charge accumulator 102 a through first read-outgate 106 a and in second charge accumulator 102 b through secondread-out gate 106 b.

Next, in the second light exposure period, according to an instructionby controller 3, pixel array controller 11 transits first read-out gate106 a from the high state (activated state) to the low state(deactivated state) at time t32 (timing of the start). Thereby, theaccumulation of the signal charge in first charge accumulator 102 a isstopped.

By the control operation described above, the signal charge generated inphotoelectric converter 101 by receiving the background light whichreaches photoelectric converter 101 after time t32 in the second lightexposure period is totally accumulated in second charge accumulator 102b through second read-out gate 106 b.

At time t33, which is the end of the second light exposure period,according to an instruction by controller 3, pixel array controller 11stops the accumulation of the signal charge in second charge accumulator102 b by transiting second read-out gate 106 b from the high state(activated state) to the low state (deactivated state), and convertslight exposure control gate 108 to an electrically conducted state bytransiting ODG from the low state (deactivated state) to the high state(activated state). Thereby, photoelectric converter 101 is reset.

At the end of the third light exposure sequence, the relationsrepresented by the following expressions are established:A2=S3A  (Expression 9)A3=S3B  (Expression 10)where the signal charge accumulated in charge accumulator 102 throughfirst read-out gate 106 a is defined as S3A, the signal chargeaccumulated in charge accumulator 102 through second read-out gate 106 bis defined as S3B, the signal charge accumulated in first chargeaccumulator 102 a is defined as A2, and the signal charge accumulatedsecond charge accumulator 102 b is defined as A3.

Furthermore, signal charge S3A is made of signal charge S3Ab generatedin photoelectric converter 101 by receiving the background light, andsignal charge S3B is made of signal charge S3Bb generated inphotoelectric converter 101 by receiving the background light.A2=S3Ab  (Expression 11)A3=S3Bb  (Expression 12)

As described above, in the third light exposure sequence, the charge isconcurrently transferred to two charge accumulators 102, i.e., firstcharge accumulator 102 a and second charge accumulator 102 b in thefirst light exposure period. For this reason, the charge amountcorresponding to about a half of the signal charge generated inphotoelectric converter 101 in the first light exposure period isaccumulated in each of charge accumulators 102.

As described for the first light exposure sequence above, there may be apossibility that the amount of the signal charge accumulated in firstcharge accumulator 102 a in the first light exposure period and that ofthe signal charge accumulated in second charge accumulator 102 b in thefirst light exposure period are not exactly 50% of the amount of thesignal charge accumulated in generated in photoelectric converter 101 inthe first light exposure period.

As illustrated in FIG. 6 , after the third light exposure sequence ends,the signal exchange drive mentioned above is again performed. After thesignal exchange drive ends, the fourth light exposure sequence isperformed. Thereby, before the fourth light exposure sequence starts,signal charge A2 accumulated in charge accumulator 102 through firstread-out gate 106 a in the third light exposure sequence is moved tosecond charge accumulator 102 b, signal charge A3 accumulated in chargeaccumulator 102 through second read-out gate 106 b is moved to firstcharge accumulator 102 a.

Next, the fourth light exposure sequence will be described. FIG. 13 is atiming chart of the fourth light exposure sequence illustrating thelight emission timing of light emitter 4, the light exposure and signalaccumulation timing in pixel section 100, and the light exposure statesof the signal charges accumulated in charge accumulators 102 throughfirst read-out gate 106 a and second read-out gate 106 b.

Similarly to the third light exposure sequence, the fourth lightexposure sequence includes a first light exposure period (also referredto as “seventh period”) having the same length as that of time Tp fromthe start of irradiation to the end of irradiation with pulsed lightfrom light emitter 4 in the first light exposure sequence and a secondlight exposure period (also referred to as “eighth period”) until timeTp passes from the end of the first light exposure period. Asillustrated in FIGS. 10 and 13 , the seventh period has the same timeinterval as that of the fifth period, and the eighth period has the sametime interval as that of the sixth period.

In the fourth light exposure sequence, the pulsed light is not emittedfrom light emitter 4.

After the fourth light exposure sequence starts, according to aninstruction by controller 3, pixel array controller 11 transits ODG fromthe high state (activated state) to the low state (deactivated state)synchronizing with time t41 at which the first light exposure periodstarts, and concurrently transits first read-out gate 106 a and secondread-out gate 106 b from the low state (deactivated state) to the highstate (activated state).

By the operation performed by pixel array controller 11, the dischargeof the signal charge from photoelectric converter 101 to overflow drain109 is stopped, and the signal charge generated in photoelectricconverter 101 by receiving the background light which reachesphotoelectric converter 101 in the first light exposure period isaccumulated in first charge accumulator 102 a through first read-outgate 106 a and in second charge accumulator 102 b through secondread-out gate 106 b.

Next, in the second light exposure period, according to an instructionby controller 3, pixel array controller 11 transits second read-out gate106 b from the high state (activated state) to the low state(deactivated state) at time t42 (timing of the start). Thereby, theaccumulation of the signal charge in second charge accumulator 102 b isstopped.

By the control operation described above, the signal charge generated inphotoelectric converter 101 by receiving the background light whichreaches photoelectric converter 101 after time t42 in the second lightexposure period is totally accumulated in first charge accumulator 102 athrough first read-out gate 106 a.

At time t43, which is the end of the second light exposure period,according to an instruction by controller 3, pixel array controller 11stops the accumulation of the signal charge in first charge accumulator102 a by transiting first read-out gate 106 a from the high state(activated state) to the low state (deactivated state), and convertslight exposure control gate 108 to an electrically conducted state bytransiting ODG from the low state (deactivated state) to the high state(activated state). Thereby, photoelectric converter 101 is reset.

At the end of the fourth light exposure sequence, signal charge A3accumulated in the third light exposure sequence is accumulated in firstcharge accumulator 102 a, and signal charge A2 accumulated in the thirdlight exposure sequence is accumulated in second charge accumulator 102b; thus, signal charge A0 and signal charge A1 after the end of thefourth light exposure sequence have the relations represented by thefollowing expressions:A2=S3A+S4B  (Expression 13)A3=S3B+S4A  (Expression 14)where the signal charge accumulated in charge accumulator 102 throughfirst read-out gate 106 a is defined as S4A, and the signal chargeaccumulated in charge accumulator 102 through second read-out gate 106 bis defined as S4B.

Furthermore, signal charge S4A is made of signal charge S4Ab generatedin photoelectric converter 101 by receiving the background light, andsignal charge S4B is made of signal charge S4Bb generated inphotoelectric converter 101 by receiving the background light. Thus, therelations represented by the following expressions are established:A2=(S3Ab+S4Bb)  (Expression 15)A3=(S3Bb+S4Ab)  (Expression 16)

Signal charge A2 obtained as a result of the third light exposuresequence and the fourth light exposure sequence is made of a componentobtained through addition average of signal charge S1Ab accumulatedthrough first read-out gate 106 a and signal charge S2Bb accumulatedthrough second read-out gate 106 b out of the signal charges generatedin photoelectric converter 101 by receiving the background light in thefirst light exposure periods of the third and fourth light exposuresequences. Such a configuration provides signal charge A2 obtained as aresult of the third light exposure sequence and the fourth lightexposure sequence as a signal charge such that the differences intransfer properties caused by a variation in properties in thesemiconductor production process between first read-out gate 106 a andsecond read-out gate 106 b are smoothed and cancelled.

Similarly to signal charge A2, this configuration also provides signalcharge A3 obtained as a result of the third light exposure sequence andthe fourth light exposure sequence as a signal charge such that thedifferences in transfer properties caused by a variation in propertiesin the semiconductor production process between first read-out gate 106a and second read-out gate 106 b are smoothed and cancelled.

Next, reading-out of the non-irradiation light exposure signal will bedescribed.

In the reading-out of the non-irradiation light exposure signal, signalcharges A2 and signal charges A3 obtained in respective pixel sections100 by performing the third light exposure sequence and the fourth lightexposure sequence are output from solid-state imaging device 10 tosignal processor 2. This step is started immediately after the fourthlight exposure sequence is completed.

The reading-out of the non-irradiation light exposure signal is the stepsimilar to the reading-out of the irradiation light exposure signaldescribed above. In other words, in the reading-out of thenon-irradiation light exposure signal, all the pixel signals A1 and allthe pixel signals A3 corresponding to pixel sections 100 are output fromsolid-state imaging device 10 through output buffer 15 by rasterscanning, and all the pixel signals A1 and all the pixel signals A3which are output are retained by signal processor 2.

Next, the calculation of the distance will be described.

The calculation of the distance is a step of calculating distance signalDout corresponding to each of pixel sections 100 from pixel signals A0,pixel signals A1, pixel signals A2, and pixel signals A3 retained bysignal processor 2 in the reading-out of the irradiation light exposuresignal and in the reading-out of the non-irradiation light exposuresignal.

As a first procedure, signal processor 2 calculates pixel signal A0 cfrom (Expression 17) where the background light component is removedfrom pixel signal A0 corresponding to each pixel section 100, andcalculates pixel signal A1 c from (Expression 18) where the backgroundlight component is removed from pixel signal A1.A0c=A0−A2  (Expression 17)A1c=A1−A3  (Expression 18)

(Expression 17) can be transformed into (Expression 19) below from(Expression 7) and (Expression 15), and (Expression 18) can betransformed into (Expression 20) below from (Expression 8) and(Expression 16):A0c=(S1Ar+S2Br)+(S1Ab+S2Bb)−(S3Ab+S4Bb)   (Expression 19)A1c=(S1Br+S2Ar)+(S1Bb+S2Ab)−(S3Bb+S4Ab)   (Expression 20)

Here, the combination of pixel signal S1Ab and pixel signal S3Ab and thecombination of pixel signal S2Bb and pixel signal S4Bb in (Expression19) are combinations of signals which correspond to the background lightcomponents obtained from the same read-out gate 106 under the sameaccumulation condition and which have the same amount. Thus, the resultof subtraction of the second term and the third term in (Expression 19)is zero, and (Expression 19) can be represented by (Expression 21).Thus, pixel signal A0 c obtained from calculation of (Expression 17)corresponds to a pixel signal obtained by removing the background lightcomponent from pixel signal A0.A0c=(S1Ar+S2Br)  (Expression 21)

Focusing on the combination of pixel signal S1Bb and pixel signal S3Bband that of pixel signal S2Ab and pixel signal S4Ab, (Expression 20) canbe represented by (Expression 22) as above. Thus, pixel signal A1 cobtained from calculation of (Expression 18) corresponds to a pixelsignal obtained by removing the background light component from pixelsignal A1.A1c=(S1Br+S2Ar)  (Expression 22)

As a second procedure, using pixel signal A0 c and pixel signal A1 cobtained from (Expression 17) and (Expression 18), signal processor 2calculates Dout from (Expression 23) where constant K is used, asfollows. Dout calculated from (Expression 23) is equivalent to(Expression 2), and is apparently a distance signal corresponding to thedistance to the subject.Dout=K×(A1c−A0c)/(A1c+A0c)  (Expression 23)

Constant K in (Expression 23) corresponds to c×Tp/2 in (Expression 2),and is desirably set according to the finite dynamic range of distancesignal Dout.

Apparently from the description of Embodiment 1 above, imaging apparatus1 operates with low electric power without preparative distancemeasurement, and can suppress saturation of the signal charge ofreflected light reflected from a subject (including a moving subject) ina short distance. Imaging apparatus 1 can also provide highly precisedistance information to the subject from which errors caused by avariation in the semiconductor production process are removed.

Although the timing of the start of the first light exposure periodtemporally matches the start of irradiation of the pulsed light by lightemitter 4 and the timing of the end of the first light exposure periodtemporally matches the timing of the start of the second light exposureperiod in the illustration in Embodiment 1, the illustration should notbe construed as limitations to the present disclosure.

For example, even if the phase of the timing of the first light exposureperiod and that of the timing of the second light exposure period aretemporally shifted ahead or behind with respect to the phase of theirradiation light, monotonically increasing distance information havingan intercept can be obtained, in principle, for a change in distance ofthe subject.

For example, the first light exposure period can be ended earlier bytime Ts than the timing of stop of the irradiation light, first read-outgate 106 a and second read-out gate 106 b can be deactivatedsynchronizing with the end of the first light exposure period, andread-out gate 106 can be reactivated after time Ts. In this case,monotonically increasing distance information can be obtained for achange in distance of the subject where the measurable distance rangefalls within the range represented by (c×(Tp−Ts)/2).

Embodiment 2

The imaging apparatus according to Embodiment 2 will now be described.While the imaging apparatus has the same configuration as that ofimaging apparatus 1 according to Embodiment 1, the imaging apparatusperforms a modified first light exposure sequence rather than the firstlight exposure sequence, a modified second light exposure sequencerather than the second light exposure sequence, a modified third lightexposure sequence rather than the third light exposure sequence, and amodified fourth light exposure sequence rather than the fourth lightexposure sequence.

Initially, the modified first light exposure sequence will be described.

FIG. 14 is a timing chart of the modified first light exposure sequenceillustrating the light emission timing of light emitter 4, the lightexposure and signal accumulation timing in pixel section 100, and thelight exposure states of the signal charges accumulated in chargeaccumulators 102 through first read-out gate 106 a and second read-outgate 106 b.

The modified first light exposure sequence includes a zeroth lightexposure period (not illustrated) until time Ts passes from the start ofirradiation with the pulsed light from light emitter 4 having a timingcontrolled by controller 3, a first light exposure period (also referredto as “first period”) from the point of time at which time Ts has passedto the end of irradiation with the pulsed light, and a second lightexposure period (also referred to as “second period”) until time Tppasses from the end of irradiation with the pulsed light. As illustratedin FIG. 14 , the first period starts before the irradiation with thepulsed light by light emitter 4 stops. The second period is a periodsubsequent to the first light exposure period. In this period, the timeinterval between the start of the first light exposure period and theend of the second period is longer than emission period Tp of the pulsedlight.

After the modified first light exposure sequence starts, according to aninstruction by controller 3, the pulsed light having an interval of timeTp is emitted from light emitter 4. The reflected light of the emittedpulsed light reflected from the subject reaches pixel section 100 aftera delay of time Td according to the distance from imaging apparatus 1,and is converted to a signal charge in photoelectric converter 101.

According to an instruction by controller 3, pixel array controller 11transits ODG from the high state (activated state) to the low state(deactivated state) synchronizing with time t11 at which the zerothlight exposure period starts, and concurrently transits first read-outgate 106 a from the low state (deactivated state) to the high state(activated state).

According to an instruction by controller 3, pixel array controller 11transits second read-out gate 106 b from the low state (deactivatedstate) to the high state (activated state) at a timing at which time Tshas passed from t11.

By the operation of pixel array controller 11, about a half of thesignal charge generated by receiving the reflected light of the pulsedlight which is emitted from light emitter 4 and reaches photoelectricconverter 101 in the first light exposure period is accumulated in firstcharge accumulator 102 a through first read-out gate 106 a, and about ahalf thereof is accumulated in second charge accumulator 102 b throughsecond read-out gate 106 b. In contrast, the signal charge generated byreceiving the background light in the zeroth light exposure period isaccumulated only in first charge accumulator 102 a through firstread-out gate 106 a, and about a half of the signal charge generated byreceiving the background light component in the first period isaccumulated in first charge accumulator 102 a through first read-outgate 106 a and about a half thereof is accumulated in second chargeaccumulator 102 b through second read-out gate 106 b.

The operation in the second light exposure period of the modified firstlight exposure sequence is the same as that in the second light exposureperiod of the first light exposure sequence according to Embodiment 1.

Next, the modified third light exposure sequence will be described.

FIG. 15 is a timing chart of the modified third light exposure sequenceillustrating the light emission timing of light emitter 4, the lightexposure and signal accumulation timing in pixel section 100, and thelight exposure states of the signal charges accumulated in chargeaccumulators 102 through first read-out gate 106 a and second read-outgate 106 b.

The modified third light exposure sequence includes a zeroth lightexposure period (not illustrated) having the same length as that of timeTs in the modified first light exposure sequence, a first light exposureperiod (also referred to as “third period”) until time (Tp−Ts) passesfrom the end of the zeroth light exposure period, and a second lightexposure period (also referred to as “fourth period”) until time Tppasses from the end of the first light exposure period. As illustratedin FIGS. 14 and 15 , the third period has the same time interval as thatof the first period, and the fourth period has the same time interval asthat of the second period.

In the modified third light exposure sequence, the pulsed light is notemitted from light emitter 4.

After the modified third light exposure sequence starts, according to aninstruction by controller 3, pixel array controller 11 transits ODG fromthe high state (activated state) to the low state (deactivated state)synchronizing with time t31 at which the zeroth light exposure periodstarts, and concurrently transits first read-out gate 106 a from the lowstate (deactivated state) to the high state (activated state).

According to an instruction by controller 3, pixel array controller 11transits second read-out gate 106 b from the low state (deactivatedstate) to the high state (activated state) at a timing at which time Tshas passed from t31.

By the operation of pixel array controller 11, the signal chargegenerated by receiving the background light in the zeroth light exposureperiod is accumulated only in first charge accumulator 102 a throughfirst read-out gate 106 a, and about a half of the signal chargegenerated by receiving the background light component in the firstperiod is accumulated in first charge accumulator 102 a through firstread-out gate 106 a and about a half thereof is accumulated in secondcharge accumulator 102 b through second read-out gate 106 b.

The operation in the second light exposure period of the modified thirdlight exposure sequence is the same as that in the second light exposureperiod of the third light exposure sequence according to Embodiment 1.

Signal charge A0′ obtained in first charge accumulator 102 a in themodified first light exposure sequence is made of signal charge S1Cr,which is generated in photoelectric converter 101 by receiving an earlyarriving component of the reflected light of the pulsed light emittedfrom light emitter 4 which reaches photoelectric converter 101 in thefirst light exposure period, and signal charge S1Cb generated inphotoelectric converter 101 by receiving the background light other thanthe reflected light reaching in the first light exposure period.

Signal charge A2′ obtained in first charge accumulator 102 a in themodified third light exposure sequence is made of signal charge S3Cbgenerated in photoelectric converter 101 by receiving the backgroundlight other than the reflected light reaching there in the first lightexposure period. Because this signal charge S3Cb is a component obtainedfrom the same first read-out gate 106 a under the same accumulationcondition as those of signal charge S1Cb above, the background lightcomponent is removed from signal charge A0 c′ determined by (Expression24):A0c′=A0′−A2′(=S1Cr+S1Cb−S3Cb)  (Expression 24)

For signal charge A1′ obtained in second charge accumulator 102 b in themodified first light exposure sequence and signal charge A3′ obtained insecond charge accumulator 102 b in the modified third light exposuresequence, signal charge S1Db as a background light component is equal tosignal charge S3Db as a background light component as described above.Thus, the background light component is removed from signal charge A1 c′determined from (Expression 25):A1c′=A1′−A3′(=S1Dr+S1Db−S3Db)  (Expression 25)

As described above, a pixel signal from which the background light iscorrectly removed can be obtained even if the start of activation ofsecond read-out gate 106 b is delayed by time Ts with respect to theactivation timing of first read-out gate 106 a. Thus, in the modifiedsecond light exposure sequence and the modified fourth light exposuresequence, the distance signal calculated by signal processor 2 in thesame way as that in Embodiment 1 is also obtained in the same way asabove from the pixel signal obtained with a delayed start of secondread-out gate 106 b by time Ts.

Compared to pixel signal A0′, pixel signal A1 is exposed to light for alonger time, which results in a relatively larger signal amount and thusreduces the received component of the background light. Thus, signalsaturation in charge accumulator 102 is further suppressed in theimaging apparatus according to Embodiment 2.

To be noted, in the case where the closest measurable distance requiredis defined as Dcl, time Tp is desirably set in a range satisfying(Expression 26) below:Ts<2×Dcl/c  (Expression 26)

The right side of (Expression 26) corresponds to the round-trip time oflight to a subject in distance Dcl.

Embodiment 3

The imaging apparatus according to Embodiment 3 will now be described.This imaging apparatus includes pixel section 100 b, rather than pixelsection 100 included in imaging apparatus 1 according to Embodiment 1.In the description below, identical reference signs will be given tocomponents of the imaging apparatus according to Embodiment 3 identicalto those of pixel section 100 according to Embodiment 1, and thedetailed description thereof will be omitted because those have beenalready described.

FIG. 16 is a schematic view illustrating an example of the configurationof pixel section 100 b.

Unlike pixel section 100 according to Embodiment 1 including fivetransfer electrodes 105 (transfer electrodes 105 a, 105 b, 105 c, 105 d,and 105 e) (see FIG. 5 ), pixel section 100 b includes ten transferelectrodes 105 (transfer electrodes 105 a, 105 b, 105 c, 105 d, 105 e,105 f, 105 g, 105 h, 105 i, and 105 j) as illustrated in FIG. 16 .

In the present embodiment, voltages VG1, VG2, VG3, VG4, VG5, VG6, VG7,VG8, VG9, and VG0 are applied to transfer electrodes 105 (transferelectrodes 105 a, 105 b, 105 c, 105 d, 105 e, 105 f, 105 g, 105 h, 105i, and 105 j), respectively.

In such a configuration, four separated charge accumulators 102 (here,first charge accumulator 102 a, second charge accumulator 102 b, thirdcharge accumulator 102 c, and fourth charge accumulator 102 d) can beformed in one pixel section 100 b.

First charge accumulator 102 a, second charge accumulator 102 b, thirdcharge accumulator 102 c, and fourth charge accumulator 102 d are formedbelow transfer electrodes 105 in the depth directions thereof (here,below transfer electrodes 105 a, 105 c, 105 e, and 105 g in the depthdirections) under high voltages VG1, VG3, VG5, and VG7 applied by pixelarray controller 11.

First charge accumulator 102 a and second charge accumulator 102 b areadjacent to first read-out gate 106 a and second read-out gate 106 b,respectively. The signal charge generated in photoelectric converter 101is accumulated in first charge accumulator 102 a and second chargeaccumulator 102 b through first read-out gate 106 a and second read-outgate 106 b in the activated state.

FIG. 17 is an operation sequence diagram illustrating an operationperformed by the imaging apparatus according to Embodiment 3.

As illustrated in FIG. 17 , the imaging apparatus according toEmbodiment 3 sequentially performs steps included in a first lightexposure sequence, first signal charge exchange drive, a second lightexposure sequence, signal charge move, a third light exposure sequence,second signal charge exchange drive, a fourth light exposure sequence,signal read-out, and calculation of a distance.

The first light exposure sequence, the second light exposure sequence,the third light exposure sequence, the fourth light exposure sequence,and the calculation of the distance according to Embodiment 3 areidentical to those according to Embodiment 1.

Because the signal charges can be accumulated in four places in pixelsection 100 b in the imaging apparatus according to Embodiment, signalcharges A0, A1, A2, and A3 can be continuously generated without beingread out halfway.

FIG. 18 is a schematic plan view illustrating the arrangement relationamong signal charges A0, A1, A2, and A3.

In FIG. 18 , the first state of the charge accumulator indicates thepositional relation in arrangement of the signal charges at time tt41 atwhich the first light exposure sequence is completed, the second stateof the charge accumulator indicates the positional relation inarrangement of the signal charges at time tt42 at which the second lightexposure sequence starts, the third state of the charge accumulatorindicates the positional relation in arrangement of the signal chargesat time tt43 at which the third light exposure sequence is completed,and the fourth state of the charge accumulator indicates the positionalrelation in arrangement of the signal charges at time tt44 at which thefourth light exposure sequence starts.

In the first signal charge exchange drive, the positional relationbetween signal charge A0 and signal charge A1 is changed from the firststate of the charge accumulator to the second state of the chargeaccumulator by 10-phase drive control of transfer electrode 105 andvoltage control of transfer control gate 112 and charge retention gate111 similar to that in Embodiment 1 by pixel array controller 11.

In the signal charge move, signal charges A0, A1, A2, and A3 are movedupwardly by five electrodes by drive control of transfer electrode 105by pixel array controller 11 to change the second state of the chargeaccumulator to the third state of the charge accumulator.

In the second signal charge exchange drive, the positional relationbetween signal charge A2 and signal charge A3 is changed from the thirdstate of the charge accumulator to the fourth state of the chargeaccumulator by the 10-phase drive control of transfer electrode 105 andthe voltage control of transfer control gate 112 and charge retentiongate 111 similar to that in Embodiment 1 by pixel array controller 11.

In the signal read-out, signal charges A0, A1, A2, and A3 obtained ineach pixel section 100 b by the first light exposure sequence to thefourth light exposure sequence are read out, and pixel signals A0, A1,A2, and A3 of all the pixel sections 100 b are output from solid-stateimaging device 10 to signal processor 2. In other words, whilehorizontal scanner 14 is performing horizontal scan, pixel arraycontroller 11 and vertical scanner 12 successively output signal chargesA0, A1, A2, and A3 from a column of pixel sections 100 b to columnprocessor 13 to output all the pixel signals A0, A1, A2, and A3 from thecolumn of pixel sections 100 b in a continuous horizontal synchronizingperiod. Thereafter, the output processing is performed on another columnof pixel sections 100 b to output pixel signals A0, A1, A2, and A3corresponding to all the pixel sections 100 b from solid-state imagingdevice 10.

The imaging apparatus according to Embodiment 3 including pixel section100 b having the above-mentioned configuration and performing theabove-mentioned operation can output pixel signals A0, A1, A2, and A3having the same properties as those in Embodiment 1, in batch, after thefourth light exposure sequence. This shortens the difference in timebetween the first light exposure sequence and the second light exposuresequence and the difference in time between the third light exposuresequence and the fourth light exposure sequence. For this reason, theimaging apparatus according to Embodiment 3 can remove the backgroundlight with higher precision under circumstances where the backgroundlight temporally changes, in particular.

Furthermore, apparently, the imaging apparatus according to Embodiment 3can input all the pixel signals A0, A1, A2, and A3 corresponding to acolumn of pixel sections 100 b to signal processor 2 in the horizontalsynchronizing period including four continuous periods. Thus, signalprocessor 2 does need to include a frame buffer which records andretains four different pixel signals, and can perform pipelineprocessing with line buffers for three or four columns, each of the linebuffer retaining pixel signals A0, A1, A2, and A3 corresponding to fourcolumns of pixel sections 100 b. For this reason, the imaging apparatusaccording to Embodiment 3 can start the output of the distance signal ina short time from the end of the last fourth light exposure sequencewhile it is compact.

Embodiment 4

The imaging apparatus according to Embodiment 4 will now be described.This imaging apparatus includes pixel section 100 c, rather than pixelsection 100 included in imaging apparatus 1 according to Embodiment 1.In the description below, identical reference signs will be given tocomponents of the imaging apparatus according to Embodiment 3 identicalto those of pixel section 100 according to Embodiment 1, and thedetailed description thereof will be omitted because those have beenalready described.

FIG. 19 is a schematic view illustrating an example of the configurationof pixel section 100 c.

Unlike pixel section 100 according to Embodiment 1 including fivetransfer electrodes 105 (transfer electrodes 105 a, 105 b, 105 c, 105 d,and 105 e) (see FIG. 5 ), pixel section 100 c includes seven transferelectrodes 105 (transfer electrodes 105 a, 105 b, 105 c, 105 d, 105 e,105 f, and 105 g) as illustrated in FIG. 19 .

In the present embodiment, voltages VG1, VG2, VG3, VG4, VG5, VG6, andVG7 are applied to transfer electrodes 105 a, 105 b, 105 c, 105 d, 105e, 105 f, and 105 g, respectively.

In such a configuration, three separated charge accumulators 102 (here,first charge accumulator 102 a, second charge accumulator 102 b, andthird charge accumulator 102 c) can be formed in one pixel section 100c.

First charge accumulator 102 a, second charge accumulator 102 b, andthird charge accumulator 102 c are formed below transfer electrodes 105in the depth directions thereof (here, below transfer electrodes 105 a,105 c, and 105 e in the depth directions thereof) under high voltagesVG1, VG3, and VG5 applied by pixel array controller 11.

As illustrated in FIG. 19 , pixel section 100 c includes photoelectricconverter 101 a, rather than photoelectric converter 101 in pixelsection 100 according to Embodiment 1.

Unlike pixel section 100 according to Embodiment 1 including tworead-out gates 106 (first read-out gate 106 a and second read-out gate106 b) (see FIG. 5 ), photoelectric converter 101 a includes threeread-out gates 106 (first read-out gate 106 a, second read-out gate 106b, and third read-out gate 106 c).

First charge accumulator 102 a, second charge accumulator 102 b, andthird charge accumulator 102 c are adjacent to first read-out gate 106a, second read-out gate 106 b, and third read-out gate 106 c,respectively. The signal charge generated in photoelectric converter 101is accumulated in first charge accumulator 102 a, second chargeaccumulator 102 b, and third charge accumulator 102 c through firstread-out gate 106 a, second read-out gate 106 b, and third read-out gate106 c in the activated state.

FIGS. 20 and 21 are each a timing chart of the first light exposuresequence according to Embodiment 4 illustrating the light emissiontiming of light emitter 4, the light exposure and signal accumulationtiming in pixel section 100 c, and the light exposure states of thesignal charges accumulated in charge accumulators 102 through firstread-out gate 106 a, second read-out gate 106 b, and third read-out gate106 c.

The first light exposure sequence includes a first light exposure periodsynchronizing with time Tp from the start of irradiation to the end ofirradiation with the pulsed light emitted from light emitter 4 having atiming controlled by controller 3, and a second light exposure perioduntil time Tp passes from the end of irradiation with the pulsed light,and a third light exposure period until time Tp passes from the end ofthe second light exposure period.

After the first light exposure sequence starts, according to aninstruction by controller 3, the pulsed light having an interval of timeTp is emitted from light emitter 4. The reflected light of the emittedpulsed light reflected from the subject reaches pixel section 100 cafter a delay of time Td according to the distance from the imagingapparatus according to Embodiment 4, and is converted to a signal chargein photoelectric converter 101 a.

FIG. 20 is a timing chart of case 1 where the pulsed reflected light isreceived by photoelectric converter 101 a in a period across the firstlight exposure period and the second light exposure period. FIG. 21 is atiming chart of case 2 where the pulsed reflected light is received byphotoelectric converter 101 a in a period across the second lightexposure period and the third light exposure period.

According to an instruction by controller 3, pixel array controller 11transits ODG from the high state (activated state) to the low state(deactivated state) at time t11 at which the first light exposure periodstarts, and concurrently transits first read-out gate 106 a, secondread-out gate 106 b, and third read-out gate 106 c all from the lowstate (deactivated state) to the high state (activated state).

By the operation of pixel array controller 11, discharge of the signalcharge from photoelectric converter 101 a to overflow drain 109 isstopped, and the signal charge generated in photoelectric converter 101a by receiving the reflected light of the pulsed light emitted fromlight emitter 4 which reaches photoelectric converter 101 a in the firstlight exposure period and by receiving the background light other thanthe reflected light reaching photoelectric converter 101 a in the firstlight exposure period is accumulated in first charge accumulator 102 athrough first read-out gate 106 a, in second charge accumulator 102 bthrough second read-out gate 106 b, and in third charge accumulator 102c through third read-out gate 106 c. Thereby, about one-third of thesignal charge generated in photoelectric converter 101 a is distributedto and accumulated in first charge accumulator 102 a, second chargeaccumulator 102 b, and third charge accumulator 102 c.

Next, in the second light exposure period, according to an instructionby controller 3, pixel array controller 11 transits first read-out gate106 a from the high state (activated state) to the low state(deactivated state) at time t12 (timing of the start). Thereby, theaccumulation of the signal charge in first charge accumulator 102 a isstopped.

By the operation of pixel array controller 11, the signal chargegenerated in photoelectric converter 101 by receiving the reflectedlight which reaches photoelectric converter 101 a in the second lightexposure period and by receiving the background light which reachesphotoelectric converter 101 a in the second light exposure period isaccumulated in second charge accumulator 102 b through second read-outgate 106 b and in third charge accumulator 102 c through third read-outgate 106 c. Thereby, about a half of the signal charge generated inphotoelectric converter 101 a is accumulated in second chargeaccumulator 102 b and third charge accumulator 102 c.

Next, in the third light exposure period, according to an instruction bycontroller 3, pixel array controller 11 transits second read-out gate106 b from the high state (activated state) to the low state(deactivated state) at time t13 (timing of the start). Thereby, theaccumulation of the signal charge in second charge accumulator 102 b isstopped.

By the operation of pixel array controller 11, the signal chargegenerated in photoelectric converter 101 a by receiving the reflectedlight which reaches photoelectric converter 101 a in the third lightexposure period and by receiving the background light which reachesphotoelectric converter 101 a in the third light exposure period istotally accumulated in third charge accumulator 102 c through thirdread-out gate 106 c.

At time t14, which is the end of the third light exposure period,according to an instruction by controller 3, pixel array controller 11stops the accumulation of the signal charge in third charge accumulator102 c by transiting third read-out gate 106 c from the high state(activated state) to the low state (deactivated state), and convertslight exposure control gate 108 to an electrically conducted state bytransiting ODG from the low state (deactivated state) to the high state(activated state). Thereby, photoelectric converter 101 is reset.

Hereinafter, at the end of the first light exposure sequence, the signalcharge accumulated in first charge accumulator 102 a through firstread-out gate 106 a is defined as P0, the signal charge accumulated insecond charge accumulator 102 b through second read-out gate 106 b isdefined as P1, and the signal charge accumulated in third chargeaccumulator 102 c through third read-out gate 106 c is defined as P2.

Signal charges P0, P1, and P2 are output from each pixel section 100 cto signal processor 2 by the signal charge reading-out operation aspixel signals P0, P1, and P2 in order of raster scanning, and areretained in signal processor 2.

As illustrated in FIG. 20 , in case 1 where the subject is located in arelatively close distance and the reflected light has a relatively largeintensity, about one-third of the signal charge generated inphotoelectric converter 101 a in the first light exposure period isdistributed to and accumulated in three charge accumulators 102.Thereby, signal saturation in charge accumulator 102 is furthersuppressed by the imaging apparatus according to Embodiment 4.

FIG. 22 is a timing chart of the third light exposure sequence accordingto Embodiment 4 illustrating the light exposure and signal accumulationtiming in pixel section 100 c, and the light exposure states of thesignal charges accumulated in charge accumulators 102 through firstread-out gate 106 a, second read-out gate 106 b, and third read-out gate106 c.

The third light exposure sequence includes a first light exposure periodhaving the same length as that of time Tp from the start of irradiationto the end with the pulsed light from light emitter 4 in the first lightexposure sequence, and a second light exposure period until time Tppasses from the end of the first light exposure period, and a thirdlight exposure period until time Tp passes from the end of the secondlight exposure period.

In the third light exposure sequence, the pulsed light is not emittedfrom light emitter 4.

According to an instruction by controller 3, pixel array controller 11transits ODG from the high state (activated state) to the low state(deactivated state) synchronizing with time t31 at which the first lightexposure period starts, and concurrently transits first read-out gate106 a, second read-out gate 106 b, and third read-out gate 106 c allfrom the low state (deactivated state) to the high state (activatedstate).

By the operation of pixel array controller 11, discharge of the signalcharge from photoelectric converter 101 a to overflow drain 109 isstopped, and the signal charge generated in photoelectric converter 101a by receiving the background light is accumulated in first chargeaccumulator 102 a through first read-out gate 106 a, in second chargeaccumulator 102 b through second read-out gate 106 b, and in thirdcharge accumulator 102 c through third read-out gate 106 c. Thereby,about one-third of the signal charge generated in photoelectricconverter 101 a is distributed to and accumulated in first chargeaccumulator 102 a, second charge accumulator 102 b, and third chargeaccumulator 102 c.

Next, in the second light exposure period, according to an instructionby controller 3, pixel array controller 11 transits first read-out gate106 a from the high state (activated state) to the low state(deactivated state) at time t32 (timing of the start). Thereby, theaccumulation of the signal charge in first charge accumulator 102 a isstopped.

By the operation of pixel array controller 11, the signal chargegenerated in photoelectric converter 101 a by receiving the backgroundlight which reaches photoelectric converter 101 a in the second lightexposure period is accumulated in second charge accumulator 102 bthrough second read-out gate 106 b and in third charge accumulator 102 cthrough third read-out gate 106 c. Thereby, about a half of the signalcharge generated in photoelectric converter 101 a is accumulated insecond charge accumulator 102 b and third charge accumulator 102 c.

Next, in the third light exposure period, according to an instruction bycontroller 3, pixel array controller 11 transits second read-out gate106 b from the high state (activated state) to the low state(deactivated state) at time t33 (timing of the start). Thereby, theaccumulation of the signal charge in second charge accumulator 102 b isstopped.

By the operation of pixel array controller 11, the signal chargegenerated in photoelectric converter 101 a by receiving the backgroundlight which reaches photoelectric converter 101 a in the third lightexposure period is totally accumulated in third charge accumulator 102 cthrough third read-out gate 106 c.

At time t34, which is the end of the third light exposure period,according to an instruction by controller 3, pixel array controller 11stops the accumulation of the signal charge in third charge accumulator102 c by transiting third read-out gate 106 c from the high state(activated state) to the low state (deactivated state), and convertslight exposure control gate 108 to an electrically conducted state bytransiting ODG from the low state (deactivated state) to the high state(activated state). Thereby, photoelectric converter 101 is reset.

Hereinafter, at the end of the third light exposure sequence, the signalcharge accumulated in first charge accumulator 102 a through firstread-out gate 106 a is defined as B0, the signal charge accumulated insecond charge accumulator 102 b through second read-out gate 106 b isdefined as B1, and the signal charge accumulated in third chargeaccumulator 102 c through third read-out gate 106 c is defined as B2.

Signal charges B0, B1, and B2 are output from each pixel section 100 cto signal processor 2 by the signal charge reading-out operation aspixel signals B0, B1, and B2 in order of raster scanning, and areretained in signal processor 2.

Pixel signal B0 is equal to the background light component contained inpixel signal P0 (signal charge S1Xb in FIG. 20 or FIG. 21 ), pixelsignal B1 is equal to the background light component contained in pixelsignal P1 (signal charge S1Yb in FIG. 20 or FIG. 21 ), and pixel signalB2 is equal to the background light component contained in pixel signalP2 (signal charge S1Zb in FIG. 20 or FIG. 21 ).

Signal processor 2 calculates distance signals Dout corresponding torespective pixel sections 100 c from pixel signals P0, P1, and P2 andpixel signals B0, B1, and B2 retained.

As a first procedure, signal processor 2 calculates pixel signal P0 cfrom (Expression 27) where the background light component is removedfrom pixel signal P0 corresponding to each pixel section 100 c,calculates pixel signal P1 c from (Expression 28) where the backgroundlight component is removed from pixel signal P1, and calculates pixelsignal P2 c from (Expression 29) where the background light component isremoved from pixel signal P2.P0c=P0−B0  (Expression 27)P1c=P1−B1  (Expression 28)P2c=P2−B2  (Expression 29)

As a second procedure, signal processor 2 determines whether thereflected light reflected from the subject when the first light exposuresequence is performed corresponds to case 1 where the charge isaccumulated in pixel section 100 c within the first light exposureperiod and the second light exposure period or corresponds to case 2where the charge is accumulated within the second light exposure periodand the third light exposure period, and calculates distance signalDout.

In the case where the condition represented by (Expression 30) issatisfied, it can be determined that the reflected light is not receivedin pixel section 100 c in the third light exposure period. Thus,distance signal Dout is calculated from (Expression 31):P0c≥P2c−P1c  (Expression 30)Dout=K′×(P2c+P1c−2×P0c)/(P2c+P1c+P0c)  (Expression 31)

In the case where the condition represented by (Expression 32) issatisfied, it can be determined that the reflected light is not receivedin pixel section 100 c in the first light exposure period. Thus,distance signal Dout is calculated from (Expression 33):P0c<P2c−P1c  (Expression 32)Dout=K′×{1+(P2c−P1c)/(P2c+P1c)}  (Expression 33)

In (Expression 31) and (Expression 33), K′ is a constant correspondingto c×Tp/2.

Apparently from the description about Embodiment 4 above, in the imagingapparatus according to Embodiment 4, the detection limit distance of thesubject in a long distance is c×Tp, the detection limit distance beingdetermined in principle by time Tp, which is the pulse width of theirradiation light emitted from light emitter 4. For this reason, theimaging apparatus according to Embodiment 4 can measure the distancetwice longer than that measured by imaging apparatus 1 according toEmbodiment 1 having a detection limit distance of the subject in a longdistance of c×Tp/2.

Although Embodiment 4 does not include the step corresponding to the“signal charge exchange drive” disclosed in Embodiment 1, such a stepcan be easily implemented by a technique according to the presentdisclosure (for example, a step similar to the signal charge exchangedrive in Embodiment 1) by adding four more transfer electrodes 105 atthe maximum in the configuration illustrated in FIG. 19 .

Although the imaging apparatus according to one aspect of the presentdisclosure has been described based on Embodiments 1 to 4, theseembodiments should not be construed as limitations to the presentdisclosure. One or more aspects according to the present disclosure mayalso cover a variety of modifications of these embodiments conceived andmade by persons skilled in the art and combinations of componentsincluded in different embodiments without departing from the gist of thepresent disclosure.

Although only some exemplary embodiments of the present disclosure havebeen described in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of the present disclosure. Accordingly, all suchmodifications are intended to be included within the scope of thepresent disclosure.

INDUSTRIAL APPLICABILITY

The present disclosure can be widely used in imaging apparatuses whichobtain distance images of subjects.

The invention claimed is:
 1. An imaging apparatus, comprising: a lightemitter which emits pulsed light to a subject; a solid-state imagingdevice including a pixel section disposed on a semiconductor substrate;and a signal processor which calculates distance information concerninga distance to the subject, wherein the pixel section includes: aphotoelectric converter which converts received light to a signalcharge; a first read-out gate and a second read-out gate which read outsignal charges from the photoelectric converter; and a plurality ofcharge accumulators which includes a first charge accumulator and asecond charge accumulator which are paired with the first read-out gateand the second read-out gate, respectively, and accumulates the signalcharges read out by the first read-out gate and the second read-outgate, the first read-out gate is activated in a first period whichstarts before emission of the pulsed light by the light emitter isstopped, and is deactivated in a second period subsequent to the firstperiod, a time interval between the start of the first period and an endof the second period is longer than an emission period of the pulsedlight, the second read-out gate is activated in the first period and thesecond period, the first charge accumulator accumulates the signalcharge read out by the first read-out gate activated in the firstperiod, the second charge accumulator accumulates the signal charge readout by the second read-out gate activated in the first period and thesecond period, and when the photoelectric converter receives light, thesignal processor calculates the distance information based on: a totalamount of the signal charges accumulated in the plurality of chargeaccumulators in the first period and the second period; and a differencebetween an amount of the signal charge accumulated in the second chargeaccumulator in the first period and the second period and an amount ofthe signal charge accumulated in the first charge accumulator in thefirst period.
 2. The imaging apparatus according to claim 1, wherein atiming for starting activation of the first read-out gate is identicalto a timing for starting activation of the second read-out gate.
 3. Theimaging apparatus according to claim 1, wherein a timing for startingactivation of the first read-out gate is earlier than a timing forstarting activation of the second read-out gate.
 4. The imagingapparatus according to claim 1, wherein the solid-state imaging deviceincludes pixel sections arranged in a matrix to constitute a pixelarray, each of the pixel sections being the pixel section, and in all ofthe pixel sections, the first read-out gates and the second read-outgates are disposed in identical relative positions with respect to thephotoelectric converter, and timings of activation and deactivation ofthe first read-out gates are identical, and timings of activation anddeactivation of the second read-out gates are identical.
 5. The imagingapparatus according to claim 1, wherein in a first reflected lightnon-reception period in which the photoelectric converter does notreceive reflected light of the pulsed light emitted from the lightemitter, the first read-out gate is further activated in a third periodhaving a time interval identical to a time interval of the first period,and is further deactivated in a fourth period which is subsequent to thethird period and has a time interval identical to a time interval of thesecond period, in the first reflected light non-reception period, thesecond read-out gate is further activated in the third period and thefourth period, the first charge accumulator further accumulates thesignal charge read out by the first read-out gate which is activated, inthe third period, the second charge accumulator further accumulates thesignal charge read out by the second read-out gate which is activated,in the third period and the fourth period, and the signal processorcalculates the distance information based on an amount of the signalcharge accumulated in the first charge accumulator in the third periodand an amount of the signal charge accumulated in the second chargeaccumulator in the third period and the fourth period.
 6. The imagingapparatus according to claim 1, wherein the pixel section furtherincludes a signal exchanger for use in exchanging the signal chargeaccumulated in the first charge accumulator and the signal chargeaccumulated in the second charge accumulator between the first chargeaccumulator and the second charge accumulator, the light emitter furtherreemits the pulsed light to the subject after exchanging the signalcharge accumulated in the first charge accumulator and the signal chargeaccumulated in the second charge accumulator using the signal exchanger,the second read-out gate is further activated in a fifth period where aphase difference in the fifth period with respect to reemission of thepulsed light by the light emitter is equal to a phase difference in thefirst period with respect to the pulsed light by the light emitter, andis further deactivated in a sixth period where a phase difference in thesix period with respect to reemission of the pulsed light by the lightemitter is equal to a phase difference in the second period with respectto emission of the pulsed light by the light emitter, the first read-outgate is further activated in the fifth period and the sixth period, thefirst charge accumulator further accumulates the signal charge read outby the first read-out gate which is activated, in the fifth period andthe sixth period, the second charge accumulator further accumulates thesignal charge read out by the second read-out gate which is activated,in the fifth period, and when the photoelectric converter furtherreceives light, the signal processor calculates the distance informationbased on: a total amount of the signal charges accumulated in theplurality of charge accumulators in the first period, the second period,the fifth period, and the sixth period; and a difference between a totalamount of the signal charges accumulated in the second chargeaccumulator in the first period and the second period and the signalcharges accumulated in the first charge accumulator in the fifth periodand the sixth period and a total amount of the signal charge accumulatedin the first charge accumulator in the first period and the signalcharge accumulated in the second charge accumulator in the fifth period.7. The imaging apparatus according to claim 6, wherein in a secondreflected light non-reception period in which the photoelectricconverter does not receive reflected light of the pulsed light reemittedfrom the light emitter, the second read-out gate is further activated ina seventh period having a time interval identical to a time interval ofthe fifth period, and is further deactivated in an eighth period whichis subsequent to the seventh period and has a time interval identical toa time interval of the sixth period, in the second reflected lightnon-reception period, the first read-out gate is further activated inthe seventh period and the eighth period, the first charge accumulatorfurther accumulates the signal charge read out by the first read-outgate which is activated, in the seventh period and the eighth period,the second charge accumulator further accumulates the signal charge readout by the second read-out gate which is activated, in the seventhperiod, and the signal processor calculates the distance informationbased on an amount of the signal charge accumulated in the first chargeaccumulator in the seventh period and the eighth period and an amount ofthe signal charge accumulated in the second charge accumulator in theseventh period.
 8. The imaging apparatus according to claim 1, whereinthe plurality of charge accumulators further includes a third chargeaccumulator and a fourth charge accumulator which are paired with thefirst read-out gate and the second read-out gate, respectively.
 9. Adistance information calculation method which is performed by an imagingapparatus including: a light emitter which emits pulsed light to asubject; a solid-state imaging device including a pixel section disposedon a semiconductor substrate; and a signal processor which calculatesdistance information concerning a distance to the subject, the pixelsection including a photoelectric converter which converts receivedlight to a signal charge, a first read-out gate and a second read-outgate which read out signal charges from the photoelectric converter, aplurality of charge accumulators which includes a first chargeaccumulator and a second charge accumulator which are paired with thefirst read-out gate and the second read-out gate, respectively, andaccumulates the signal charges read out by the first read-out gate andthe second read-out gate, the distance information calculation methodcomprising: activating the first read-out gate in a first period whichstarts before emission of the pulsed light by the light emitter isstopped, and deactivating the first read-out gate in a second periodsubsequent to the first period, where a time interval between the startof the first period and an end of the second period is longer than anemission period of the pulsed light; activating the second read-out gatein the first period and the second period; accumulating the signalcharge read out by the first read-out gate which is activated, in thefirst charge accumulator in the first period; accumulating the signalcharge read out by the second read-out gate which is activated, in thesecond charge accumulator in the first period and the second period; andcalculating the distance information based on: a total amount of thesignal charges accumulated in the plurality of charge accumulators inthe first period and the second period, and a difference between anamount of the signal charge accumulated in the second charge accumulatorin the first period and the second period and an amount of the signalcharge accumulated in the first charge accumulator in the first periodwhen the photoelectric converter receives light.